Do Refined Sugars Cause Fusel Alcohols?

[Brudru]

I've been doing a fair bit of studying into Fusel Alcohols and I'm fairly happy with everything I've learnt so far and think I have a decent grasp of most of the causes and how to avoid them. One thing that struck me as odd however and I haven't been able to corroborate it is that refined sugars can be a cause for fusel alcohols?

http://www.brewstore.co.uk/wp/wp-co...wing-diagnosis-of-off-flavours-and-smells.pdf
This chart claims that you should not use refined sugars and yet I've seen many a home-brewer around articles, forums, reddit say that using sucrose/table sugar is fine but that most people prefer dextrose. Never seen anybody mention yet that table sugar causes fusels.

 

[Sadfield]

Dextrose is heavily refined sugar from corn, and only possibly preferred for providing less flavour than beet or cane sugar. Although it eliminates one extra job for yeast to do breaking sucrose down into monosaccharides, glucose and fructose.

Fusels, higher alcohols are byproducts of fermentation and more likely to be noticable in higher gravity beers.

Probably a throw back from people dumping a load into beers to boost abv, with very little fermentation control. More work for stressed yeast, but not an issue under normal, healthy conditions.

 

[chthon]

British and Belgian brewers have used historically many types of sugars, both in light and heavy beers. They wouldn't have done this if this statement was correct.

 

[obscure]

I’m actually kind of curious about exactly what they mean by refined sugar but could by some definitions even the sugars extracted from your malted barley be considered refined?

 

[trueblue]

Personally I always use invert sugar and I seem to remember a few years back reading yeast prefer cane sugar to beet sugar.

 

[Brudru]

Probably a throw back from people dumping a load into beers to boost abv, with very little fermentation control. More work for stressed yeast, but not an issue under normal, healthy conditions.

This sounds like the most likely reason - For me, I've realised half the battle in learning homebrewing is seperating old outdated/misconstrued data from the new and articles echo'ing it like its gospel

Thanks for all the input folks!

 

[Hop_it]

I've heard mentioned issues with fusel alcohols quite a few times, but fortunately I've never encountered the problem myself. However, I decided to have a look at my brewing bible, i.e. John Palmer's "How to Brew", and he makes a few suggestions on how to avoid the problem:

• increase pitching rate to limit excessive yeast growth, and to reduce stress on the yeast
• pitch when the wort is cool (also to reduce stress on the yeast)
• ferment at a lower temperature within the suggested range for the yeast
• don't add sucrose or other sugars to the wort

To me the first 3 make good sense, but the last one is obviously up for discussion. As already stated there are a lot of British and Belgian beers that utilise refined sugars in the recipe. I can only guess that the potential for developing excessive fusel alcohols depends to some extent on the recipe, and therefore the proportion of refined sugars to malt sugars. If this is small then the risk is probably low. Most strong Belgian beers using candy sugars for flavouring and colour would fall into this category

 

[chthon]

Personally I always use invert sugar and I seem to remember a few years back reading yeast prefer cane sugar to beet sugar.

The thing is, they are both sucrose. Cane sugar is made from unrefined cane juice. However, it can be refined, just like beet juice, into the white crystalline stuff that is pure sucrose. These processes different by-products. Molasses from cane sugar refining is yummy, molasses from beet sugar refining is cattle food. Unrefined beet sugar is not really ever used. But producers like Candico have their own processes to turn beet sugar into dark brown sugar and light brown sugar. And I suppose, because of the taste, that dark Candico syrup is a mix of refined beet sugar and cane molasses.

What might be possible is that cane sugar contains things that are effectively yeast nutrients, while refined beet sugar only contains pure sucrose.

 

[chthon]

I've heard mentioned issues with fusel alcohols quite a few times, but fortunately I've never encountered the problem myself. However, I decided to have a look at my brewing bible, i.e. John Palmer's "How to Brew", and he makes a few suggestions on how to avoid the problem:

• increase pitching rate to limit excessive yeast growth, and to reduce stress on the yeast
• pitch when the wort is cool (also to reduce stress on the yeast)
• ferment at a lower temperature within the suggested range for the yeast
• don't add sucrose or other sugars to the wort

To me the first 3 make good sense, but the last one is obviously up for discussion. As already stated there are a lot of British and Belgian beers that utilise refined sugars in the recipe. I can only guess that the potential for developing excessive fusel alcohols depends to some extent on the recipe, and therefore the proportion of refined sugars to malt sugars. If this is small then the risk is probably low. Most strong Belgian beers using candy sugars for flavouring and colour would fall into this category

The problem with John Palmer's answers are that it depends upon the use case.

• You don't have to overstress your yeast of course, but Belgian brewing seems to be based upon stressing yeast a bit. Underpitching (a bit) is used by Westmalle and Duvel. I don't know how the historical pitching rates of British brewers compare.
• Pitch when the wort is cool, but also, compare this with British brewing traditions (as nicely documented by Ronald Pattinson), where the pitching temperature actually depends upon the strength of the wort, and they let the temperature rise (but not too much, by using attemperators)
• Westvleteren is an example of a beer where the temperature is let loose, also Caracole does this. Other examples can be found.

The only yeast that I have actually had a bit if fusel, solventy taste was the S-33. Actually, since it was not much, I liked it that way. It was a strong beer, something like a British strong ale or barley wine. But after a couple of months of maturing it disappeared. So is the lesson here, don't ferment too warm, or let a big beer condition for a couple of months?

 

[Hop_it]

The problem with John Palmer's answers are that it depends upon the use case.

• You don't have to overstress your yeast of course, but Belgian brewing seems to be based upon stressing yeast a bit. Underpitching (a bit) is used by Westmalle and Duvel. I don't know how the historical pitching rates of British brewers compare.
• Pitch when the wort is cool, but also, compare this with British brewing traditions (as nicely documented by Ronald Pattinson), where the pitching temperature actually depends upon the strength of the wort, and they let the temperature rise (but not too much, by using attemperators)
• Westvleteren is an example of a beer where the temperature is let loose, also Caracole does this. Other examples can be found.

The only yeast that I have actually had a bit if fusel, solventy taste was the S-33. Actually, since it was not much, I liked it that way. It was a strong beer, something like a British strong ale or barley wine. But after a couple of months of maturing it disappeared. So is the lesson here, don't ferment too warm, or let a big beer condition for a couple of months?

Interesting. . . . . . . . I'm not at all sure what the answer is. I think that most homebrewers would agree that big beers benefit from some aging, but the issue of fermentation temperature is always going to depend on what you hope to achieve in your finished beer, and the ability to steer that path successfully depends largely on experience.
I recently brewed a very experimental Belgian Blond style ale using S-33. It came out with an ABV of ~6%, so not a big beer. I fermented it at ~20degC. I achieved the typical phenolic Belgium taste and smell, although not as pronounced as say a Leffe. However, I did not get any hint of higher alcohols . . . . . But perhaps I'm just not that sensitive to it.

 

[chthon]

@Hop_it : To clarify, I think my beer with S-33 reached a higher temperature, 22° on the outside so maybe 24° on the inside. But I have that with other beers too, and the S-33 is the only one that I have experience with which seems to produce this solventy taste in those circumstances.

 

[Tony Palmer]

Fusel oils can be created by the type of yeast selection. General rule is the higher the OG the greater the fusel oil production. Refined sugar has little effect it's the gravity. However fermentation is in itself a cleansing process so less pure sugar material does not necessarily increase fusel oil and acetate ester production. That said flavour taints do carry through, but for home brewers late addition of sugar syrup to a fermentation can be a useful technique.

 

[PhilBrew]

Refined sugar has little effect it's the gravity.

... erm, surely an oversimplification? You have to recognise that when you add a load of refined sugar, rather than increasing the gravity by upping the quantity of mashed malt, say, you're not just raising the gravity of the wort to be fermented but (effectively, per yeast cell needed to ferment that wort) reducing the other nutrients available to the yeast, including relative nitrogen levels, which can effect fusel alcohol production

You also change the makeup of the yeast and thus change the way the yeast will metabolise that wort ... the below is from my copy of "Yeast" by Chris White and Jamil Zainasheff, p22-23 in a section on Yeast Metabolism ...

Because yeast utilize some sugars more easily than others, they take up sugar in a specific order, with simpler sugars first: glucose, fructose, sucrose, maltose, and then maltotriose. Most of the sugar in a typical all-malt wort is maltose, with lesser amounts of glucose and maltotriose. Yeast take glucose into the cell through facilitated diffusion, without expending any metabolic energy. It is so easy for yeast to utilize glucose that the presence of glucose actually suppresses the yeasts ability to utilize maltose and maltotriose.

... and then later, on p68 in a section on the Fermentation Timeline, sub-section around the Exponential Growth Phase ...

While glucose makes up roughly 14 percent of wort sugars, maltose is the centerpiece. Maltose makes up about 59 percent of the sugars in the average wort, and its fermentation is part of what enables yeast to create some of the characteristic beer flavors.

... bearing in mind that mashing higher or lower is only likely to change those relative glucose and maltose percentages by around 5 percentage points either way, we need to recognise that adding (lots of) those non maltose sugars may very well be significantly changing the sugar composition of that wort and the way the (colony of) yeast will ferment it

Fusel alcohols, like so many other flavours generally described as "off flavours" in beer, can and do naturally form part of the flavour profile of beer anyway. Only when they reach certain (unacceptable) levels do they become faults ... so to the OP's original question of will adding refined sugars increase production of fusel alcohols, the answer is probably, Yes ... but to the follow up question of will that be a bad thing, the answer's more likely to be, that would depend on what you're brewing. But if your beer is tasting too hot/solvent-ish then following Palmer's advice may be a way to avoid that, in future

Cheers, PhilB

 

[Sadfield]

Exceptional post @PhilBrew, some very good points regarding nutrients and wort composition. I think when doing to things right becomes second nature, it's easy to overlook the pitfalls of missing these things.

 

[Tony Palmer]

If you take ordinary sugar and sufficent of the right nutrients and a high alcohol tolerant yeast 20% abv is quite easy with relatively low fusel oil production. In any case in most cases a maximum non malt addition of say 30% would be normal in European type beers.

 

[DocAnna]

Fusel alcohols are not formed from sugars - at all. The are formed from amino acid metabolism from proteins (The Ehrlich pathway). Since temperature will influence fusel alcohol production, it may be that previous experience of using refined sugar in wort was to increase temperature due to increased yeast metabolism when the sugar was added.

I did find a paper on the factors in a commercial brewery setting that minimised fusel alcohols in lager and maximised the more desirable esters, and taste were as follows - not that filling time applies to home brew:

Pitching rate 10 mln cells per mL; fermentation temperature 11.5 °C; aeration level 8.8 mg/L; and CCT filling time 4.5 h.

Contents of selected volatile esters and fusel alcohols and their relation to the sensory quality of a bottom-fermented lager beer fermented under high-gravity conditions (15.5 °P) were analyzed using response surface methodology (RSM, Box–Behnken design). The influence of various pitching rates (6–10 mln cells/mL), aeration levels (8–12 mgO2/mL), times (4.5–13.5 h) of filling CCTs (cylindroconical fermentation tanks; 3850 hL), and fermentation temperatures (8.5–11.5 °C) on the contents of selected esters, as well as on concentrations of amyl alcohols and on the sum of higher alcohols in beer, was determined in a commercial brewery fermentation plant. Beers produced throughout the experiments met or exceeded all criteria established for a commercial, marketed beer. Statistical analyses of the results revealed that within the studied ranges of process parameters, models with diversified significance described the concentrations of volatiles in beer. The multiple response optimization procedure analyses showed that the values of process parameters that minimized higher alcohols in beer (97.9 mg/L) and maximized its ethyl acetate (22.0 mg/L) and isoamyl acetate (2.09 mg/L) contents, as well as maximized the sensory quality of beer, (66.4 pts) were the following: Pitching rate 10 mln cells per mL; fermentation temperature 11.5 °C; aeration level 8.8 mg/L; and CCT filling time 4.5 h.

Anna

 

[Sadfield]

@DocAnna Both amino acids and carbohydrate both form the precursors to fusel alcohols within the oxoacid pool. According to Hough Briggs et al in Malting and Brewing Science Vol 2. Pages 598,599.

https://books.google.co.uk/books?id...sel alcohol carbohydrate oxoacid pool&f=false

 

[DocAnna]

@DocAnna Both amino acids and carbohydrate both form the precursors to fusel alcohols within the oxoacid pool. According to Hough Briggs et al in Malting and Brewing Science Vol 2. Pages 598,599.

https://books.google.co.uk/books?id...sel alcohol carbohydrate oxoacid pool&f=false

The amino acids are converted into a carbohydrate of sorts - a fusel aldehyde as part of the metabolic route, but the fusel alcohols are entirely derived from amino acids, but this wasn't proven till 2003 through experiments with radio-labelled carbon substrates, and until then there'd apparently been conjecture that other materials could contribute to fusel alcohols.
(Hazelwood, Lucie A et al., 2008. The Ehrlich pathway for fusel alcohol production: A century of research on Saccharomyces cerevisiae metabolism. Applied and environmental microbiology, 74(8), pp.2259–2266.)

Anna

 

[PhilBrew]

Fusel alcohols are not formed from sugars - at all.

... no one said they were ... the question isn't so much as how the yeast make them, but why/under what circumstances they do? hint: the only answer isn't when the yeast get hot

If you take ordinary sugar and sufficent of the right nutrients and a high alcohol tolerant yeast 20% abv is quite easy with relatively low fusel oil production. In any case in most cases a maximum non malt addition of say 30% would be normal in European type beers.

... yes, you can "get away with" fermenting non-malt-based sugars and not producing fusel alcohols, but look at the table the OP posted ... it's a troubleshooting guide. Palmer's not saying "never use refined sugars or you'll create unnacceptable levels of fusel alcohols and your beer will taste hot/alcoholic", he's saying "if you're producing beer that tastes hot/alcoholic, try not using refined sugars"

Cheers, PhilB

 

[DocAnna]

... no one said they were ... the question isn't so much as how the yeast make them, but why/under what circumstances they do? hint: the only answer isn't when the yeast get hot

The paper I mentioned in my first post looked at why and under what circumstances yeast completes the last step to make fusel alcohols. Answer, they do all the time but more under certain circumstances. When the levels are increased the yeasts can change behaviour to form hyphae (long thread form) rather than small yeast cells, this can be described as a defence mechanism that allows the yeast to forage for nutrients through cell elongation and invasive growth.
In a commercial lager beer setting, the things that produce more fusel alcohols of the undesirable kind (note some are desirable as contribute to positive flavour) relate to temperature, pitch rate, aeration, and filling time (turbulance/shaking time). They can also be induced by wide variation in pH, depriving yeast of nutrients or by fermenting only in fructose which is one of the sugars in sucrose. This might be where some of the idea about refined sugars has arisen, but the fusel alcohol behaviour only occurs if fructose is the only source, not one of the sources.

So back to the OP, adding refined sugar to beer wort isn't going to increase fusel alcohols, so long as it's temperature controlled, doesn't markedly alter the pitch rate required if done at the beginning, and isn't a large amount of fructose when fermentation has otherwise completed.

Anna